Even on a map Ocracoke Island looks vulnerable. One of the most remote islands in the Outer Banks, the thin strip of land can be reached only by public ferry, private boat or private plane. The island’s isolation is exactly what appeals to its year-round residents and its many summer tourists. That isolation can also create power delivery challenges.
Typically, the island gets its power through underwater cables from Cape Hatteras to the north. Those cables are at the end of a long, exposed overhead transmission line that reaches from the mainland. The power supply can get expensive, particularly during times of peak demand, like a hot summer afternoon when thousands of vacationing tourists run their air conditioning. Even during the winter, when the population is back to just the island’s several hundred residents, demand can peak during cold February mornings, triggering higher electricity costs.
A barrier island, Ocracoke is exposed to severe storms that can cause flooding, high winds and power outages. In the past, the island relied on a diesel generator owned by the North Carolina Electric Membership Corporation (NCEMC), the power supply organization for most of the state’s electric cooperatives, for back-up power.
The generator also helped when demand was very high for electricity—those cold winter mornings and hot summer days already mentioned. Supplying some of that energy with an alternative energy source, such as the generator, is a form of “peak shaving.”
While the generator is large enough to supply the demand for the community during mild weather, it can’t power the entire island during times of peak energy use. Another limitation of the generator? Diesel fuel, beyond what is stored on the island at the plant, must be transported by ferry.
NCEMC and Tideland Electric Membership Corporation, energy providers to the island, recognized these challenges and saw an opportunity to bring new energy resources and local control to the island.
To do that, the state’s electric cooperative leaders built a microgrid. Beyond supporting a goal of increased reliability, the Ocracoke microgrid allows the cooperatives to test new technologies and system components, and ultimately, better use the grid to serve cooperative members in new ways. A microgrid generally operates while connected to a wide area power grid but when there is a power interruption, the microgrid can be isolated and operate on its own using local energy sources.
NCEMC developed several concepts for renewable energy generation, battery storage, demand response, and energy efficiency to offset Ocracoke’s electrical demand. For system engineering, integration, and installation, they called on PowerSecure, a leading energy solutions provider owned by Southern Company.
PowerSecure worked with NCEMC’s grid modernization team to engineer a robust, scalable microgrid with diesel and solar generation, as well as battery storage. The microgrid also includes local controls with remote dispatch that can be operated in concert with existing and new demand management systems, including Ecobee thermostats and water heater controls deployed at homes and businesses throughout the island.
With PowerSecure as a partner, the electric cooperatives’ innovative approach creates a more reliable and resilient power system for the island, integrates new resources, and enables the cooperative to reduce demand when energy use peaks. Here we take a look at how it was done.
Ocracoke’s diesel generator is an important back-up energy supply and the power plant has been enhanced with green, renewable solar power. Solar panels mounted on the roof of the plant now provide 15kW of renewable energy as the sun moves across the sky. Placing the panels on the roof of the existing building saved valuable real estate, which is limited and expensive on the small island.
On average, land on Ocracoke Island is les than five feet above sea level. To limit the risk of equipment damage in the event of flooding during a major storm, the PowerSecure team built a raised concrete pad to serve as a platform. Side note: All of the supplies had to come by ferry and the concrete was mixed onsite. Not an easy job.
A bank of Tesla Powerpack batteries, installed by PowerSecure on the elevated concrete pad, provide local energy storage and are another component of the microgrid.
Inverter units, located at the end of each of the battery
lineups, give the system a great deal of flexibility. They enable the battery
units to be charged by sources other than the solar panels. That helps when the
days are short or the weather is poor. The batteries can connect not just to
the solar panels but also to the grid or the diesel generator, when necessary.
They charge during periods of low demand, such as late at night and early in
the morning. The electricity is available when demand peaks and power is more
expensive—or whenever back-up energy is needed.
Each nearly 4,000-pound Tesla Powerpack is made up of 16 individual lithium-ion battery pods. Built with a cooling and heating system adapted from the Tesla Model S automobile batteries, the Powerpacks can store 1 MWh of energy, which is roughly the amount of electricity used by 330 homes in one hour. That isn’t enough to power the island during an outage, but it can assist the diesel generator during its start-up, when initial demand often exceeds the generator’s capacity. That makes for a smoother transition when outages occur.
The final key features of Ocracoke’s microgrid—Ecobee thermostats and water heater controls—are found at homes and businesses throughout the island.
The Ecobee is a “smart” thermostat that saves energy for members. It also enables them to work with the cooperative to better manage the island’s electricity load when there is excessive demand or during a power emergency.
With these thermostats, the cooperative can remotely change the thermostat settings a few degrees to reduce peak electric loads. Members are informed when a demand response event occurs, and they can override thermostat adjustments at any time. Members can also monitor and control their thermostat settings remotely using their computer or a mobile device. The smart thermostats are expected to save participating customers 5-10 percent in energy consumption, while also benefitting all of the island’s inhabitants.
Water heater controls are another tool for demand response that are located within members’ homes and businesses. These controls allow the cooperative to make small adjustments in hot water temperature in the storage tanks, but allow hot water to flow when the consumer calls for it. These adjustments generally go unnoticed by consumers, but taken together, can significantly reduce power demand.
These distributed energy resources—the solar panels and batteries—were integrated by PowerSecure controls and system engineering. The integration of these resources, along with the existing diesel generator, ensures the system works together to give the island a smart, functioning microgrid that can communicate with the NCEMC utility group.
Ocracoke is on the cutting edge of a growing national trend away from large, centrally-controlled power plants to local systems using more efficient, renewable energy resources. One of the first locations in North Carolina to have a microgrid, Ocracoke’s system serves as a pilot project for electricity suppliers to learn how community microgrids can best complement the larger electric distribution system. Such creative approaches allow even isolated communities to achieve a clean, more resilient grid.